Test methods for performance-based evaluation of concrete containing iron sulfide-bearing aggregates: Development and application

Abstract

Iron sulfide-bearing aggregates are susceptible to oxidation reactions that can lead to an internal sulfate attack in concrete, causing severe concrete distress. Appropriate performance-based evaluation methods are required to formulate guidelines to solve these issues. Unfortunately, the current standards and specifications do not comprehensively include such evaluation methods. The present study attempted to develop a set of test methods to evaluate the performance of concrete containing iron sulfide-bearing aggregates. These methods include acceleration of the oxidation process, evaluation of expansion and rusting, and assessment of the severity of pop-outs and map cracks. An accelerated mortar bar expansion test was used to measure the expansion. A storing temperature of 60 °C, 80 ± 5% RH, and wetting and drying cycles of 7 cycles per two weeks (6% NaOCl or H2O with oxygen added through the pump while submerged) were found to be particularly successful for accelerating the oxidation process in the laboratory. An image processing method based on the “Otsu technique” was used to quantify rusting. The severity of the pop-outs was assessed using the frequency and average area of the pop-outs. The average crack width and total length of cracks per unit area computed using an image processing technique were also used to appraise the severity of the map crackings. The developed test methods were applied to assess the effectiveness of surface treatments with distinct functional mechanisms in controlling the oxidation rate. Surface treatments with a crystalline waterproof system covered with the acrylic polymer coating exhibited outstanding performance.

Keywords

• Iron sulfide-bearing aggregates
• Internal sulfate attack
• Performance-based evaluation
• Protection measures
• Surface treatments